Electrical testing apparatus



July 15, 1952 s. M. LLOYD 8 ELECTRICAL TESTING APPARATUS Filed Oct.- 19, 1948 1 lA/VENTOR amuom $44M ATTORNEY Patented July 15, 1952 if sbiiciifi t tdnnfrss'rm APPARATU'S I I Stanley M.Lloycl,'West Englcwood, N. J., assig'nor to Western Electric Company, Incorporated, '1. New York, NY;, a corporation of New York :3 1' This invention relates tdf electi'ueal testin 'methods" and apparatus and more particularly to apparatus and methods for detectingcr'ossed and grounded conductors in"'electrical cableslfl An'object'of this invention is'to provide anew and-efiisientmethod"of and apparatus for detecting'electrical faults.

'Inaccordance with one embodiment of this invention an apparatus for detecting-crossed or grounded conductors'in a telephone cable o'f'unconnec'ted conductors is provided with an electronic oscillator circuit that'is dormantuntil a certain amount of capacity is int'roduced be tweenthe grid end ofthe tank'cii'cuit and ground at which time the circuit-will begin too'scilla'te at anaudiofrequency which. is detected by "a loud speaker connected to the output of theloscillator. When'aM-tes'tiprobe connected to the grid end of the tank circuit-is: touchedf toanungrounded cable-conductorj-the capacity to ground of the conductor supplies the capacity required to cause the circuit to oscillate and the'signal and pitch thereofsprovide an indication of the conditionjof the conducbon g j A'complete understanding of this inventionwill berhad by referring to thezfollowing detailed'de scription taken in conjunction with the single figuredrawingwhich illustrates inidiag rammatic form one embodiment of the invention. I

As shown in the drawing-the apparatus is provided with an oscillator tube [0, a tankcir cuit l;l,coupled to..the grid and .output circuits of, the tube .I0, and a high-yoltage power supply 12, forthe'tube I0. The tube-1'0 :may beany suit able type whichwill provide oscillationsat audio-. frequencies, the oneshown being ar tetrode having; an anode [3, a screen'fgridfltxa control grid vZIL acath de,2I"and'acathode heater12'2z The'power supply [2 includes'a resistor 23;"a

filter condenser 24 and anelectronic rectifier'30 whose elements may be disposed in the envelope of the tube In. A suitable source of alternating current (not shown) for example, a conventional 115 volt A, .0. supply lineis connected to the apparatus by means of a plug 3l'. '.O ne conductor 32 from the plug 3i is connected'jto' 'the anode 33 of the rectifier-'30 and to'heater filaments 22 and I ioqqgmter 19, 1948, Serial No. 55,348

7 Claimsyli (01. 175-483) ductance coil 42 and a condenser 43, 115 coupled at one end 44 (lower end in the 'drawingltothe anode'c'ircuit of the tube 10 througha conductor '50, 'a-res'i'stor 5i and a con'duc'tor'52. At its other end 53 the tank circuit'is connected to 'a'te'st probe 54'and is coupled through a conductor 6B and a gridcouplingcondenser'fi'l to'thecontrol and'the primary winding 64' of an output-:t'rans former l0, and'the screen grid 14 receives positive voltage through: the resistor 23. v. l'second'ary winding H'of the output transformer l0 isrcon: nected to the voice coil of a loud speaker .12.,

The apparatus described will oscillate when the'proper amount of anode output of the tubeis iedfback to the, control grid-circuit-throughthe tank circuit, and theamount of feedback is-determinedby the ratioexisting between'the :capacityof the condenser and the capacity between the point 53 "and the conductor 40 or ground, as represented, by a condenser (80,. shown inlthedotted line. In thisrembodiment the con:- ,clenser 80 is the capacitance to ;ground at the probe, and the circuitponstants of the-apparatus should be such. that-it willbehdormant and, will not oscillate unless sufiicient-. capacityis introduced between the gridend 53 ofthe tank circuit and ground to provide the ratio of grid toplate voltage necessaryv to initiate and sustain oscillationsin the circuit; Preferably the inductance 42 is of the adjustable type in: order toxmore-conr yeniently meet the relative inductance requirements. The requisitecapacity to causeioscilla tions is provided when the test probe 54 ismade topontact a free conductor in a cable, which cone ductor is capacitively coupled to ground either throughan adjacent grounded conductor or .a

- cablesheath which is coupled to ground or both.

34, while the other conductor-'40 forms thenega- Such an example illustrated in the drawing wherein aplurality of free insulated conductors T3 are encased :ina metal sheath 14- which has somercouplingto ground. -All the conductorsyin a cable; willprodl ce a whistle in the loud: speaker of the same pitch; However, if a conductoris crossed with another, the capacity to groundis substantially double and the pitch of the whistlewill drop-about one-half of an octave to give an audible indication of the fault. Since nearly all persons can detect a sudcontrol grid end of saidfeedback circuit. v

'2'; Atest set fordetermining characteristics of erated in therangeof 500 to 3,000cycles per second, any person without a serious hearingimpediment wouldhave no difficulty in detecting the change.

Connection to a conductor which is connected to groundwill prevent the apparatusi'ro'r'n whistlingand-inorder toldifferentiate this condition from a completely open circuit, a potential from the plate circuit of the oscillator is applied to r g 1 5| This causes a distinctive click when the probe V is touched to a directly grounded conducto'ri It is to be understood that theabove-described arrangements are simply illustrative ofthe 'application of the principles of the invention. Nu-

merous other arrangements maybe readily devised by those skilled in'the art which willembody the principles of the invention and fall 7 within the spirit and scope thereof. z whatisclaimed isz V 1. A test set for determining characteristics of v 'electricalqapparatus wherein the capacity-to,-

coupled to said-anode, a feedback circuit coupled to said anode and .to;saidcontrol grid, and a probe. coupled to the control grid end of said feedback circuit for contacting apparatus to be tested, said" test set being adapted to emit an audible signal. when the ca'pacity-toground 50fsaid capparatus; is connected through said probe to'the electrical apparatus wherein the capacity-togroun'd' ofthe apparatus is a measure of said characteristics, said test set comprising a'normally dormant oscillator comprising an electronic discharge'device' having a control grid and'an output circuit, and a feedbackcircuit' coupled to'the control g'rid and to the outputcircuitan audible signal means coupled'to said'output, said oscillator'beingadapted to oscillate at an audio rate when a sufilcient amount'of capacity is introduced between the grid-coupledend of the feedback circuit and ground, and a test-probe connected to said anode, audible signal means coupled to saidianode, a feedback circuitcouple'd' to said anode and to said'control-g'rid, a probe coupled to the control grid end of said feedback circuit for contacting apparatus to be tested, said test set the testprobe through a relatively high resistance, V.

beingadapted to emit an audible signal when the I capacity-to-ground of said apparatus is connected through said probe to the control grid end of said feedback circuit, and means for generating an audible click in said audible signal means to indicate when said .probe contacts a direct ground,

said last means comprising aresistance connected between 'said probe and said anode to form a path from ground through said signal means to said anode-supply-means. 1

to'the grid coupled-'1 end of the feedback circuit for contacting electrical apparatus to be tested. 3. A'test set comprising 'a normally dormant oscillator 'having'a n output-, and a control grid circuit, an'audible signal means coupled to said output, and a test probe, for coupling the control gridc'ircuit to 'a'de'vice under test thereby to add the capacity-to-ground of said device to the con trol 'grid circuit thus to initiate sustained audio oscillations in said test set. I

-4; A test set comprising a normally'dormant electronic oscillator having an anode'output and a control grid circuit, an audible signal means coupled to'said output, a source of anode current coupled to-said anode output, a test probe for coupling the control-grid circuit'to a device undertest thereby to add the 'capacity-to ground bf said device to the control'grid circuit thus to initiate sustained audio-oscillationsin=said test set,' a'nd means for generating an audible click in said audible signalmeans to indicate contact 'of said test probe to direct groundfthe last means comprising a resistance connected between said probe and said anode output circuit.

6. A test set for, locating crossed; conductors. of a cable having -a grounded [conductive :sheath, which comprises an electronic:discharge'device having a control grid and an output .circuit, a feedback tank circuit-including'a capacitive reactance coupled to the control grid and the ouput circuit, audible signal means variably responsive to variable frequencies coupled wto said output circuit,-and,a test probe connected'to the gridcoupled end of the tank circuitfor contacting one of a plurality-of insulated'conductors of acable having a-grounded conductive sheath, said capaci= tive reactance of the tankcircuit being of such a value that oscillationsr'of one pitch are transmitted to the signal means when the probe'con tacts one of said conductors which is not crossed with another and oscillations of adifierentpitch are transmitted to the signal means when the test probecontacts one of the insulatedzconductors crossed with anotherjof the insulated conductors;

7. A test set, which comprises a test'probe for V test probe engages'an uncrossed one of the con ductive cores andoscillatory currents 'of adif ferentpitch "are sustained in the output circuit when'the'test probe -is'-connected to a conductive core crossed with another core. j STANLEY M. LLOYD.

REFERENCES CITED The following references are of record inthe file'of this patent: 7

' UNITED STATES "PATENTS Number i'Name' V '1 Date 793,970 7 Simon et al. Feb. '24, 1931' 1,990,085 Mudge et alk Feb. 5,1935 2,071,607 Bjorndal Feb 23,1937 2,094,351 Draperetal 'Sept."28, 1937 2,373,079 Morelock' Apr. 3,1945 2,393,717 I speaker Janj29, 1946 

